Iris pattern-based biometric systems, for both surveillance and access control have been gaining popularity in recent years. Several such systems have already been deployed in highly secure checkpoints across the globe. The primary advantage of such systems is the uniqueness of iridal patterns across people. Over the years, many works in scientific literature have proposed feature extraction and comparison schemes for this biometric and have reported very high recognition rates.
In all iris pattern-based biometric systems, a major concern is the acquisition of very well focused eye images in which relevant iris features are discernible. The acquisition process often requires significant cooperation from the subject whose eye is being imaged. For instance, the subject may be required to be positioned at a pre-defined location, at a pre-defined distance from the camera and sufficient near infra-red (NIR) illumination must be provided for acquisition. The need for such cooperation is due to the limited capture volume of these systems. The capture volume is the volume of space in front of the image acquisition system within which the subject's iris is of acceptable quality. Once the iris of the subject is within this volume, the subject typically remains in a fixed position, with limited motion, until the system acquires a good quality image. An example of a widely used commercial iris acquisition device is the LG IrisAccess 4000. This system uses voice prompts to direct the subject into the capture volume. In general, with such systems, the positioning process can seem counter intuitive for some subjects and can result in failure to acquire errors.
Other systems that have been proposed involve less cooperation from the subjects. A good example is the Iris-On-the-Move system, developed by Sarnoff Corporation. In this system, iris patterns are captured while the subject walks through a portal fitted with NIR illumination panels. The subject stand-off required by the system is 3 meters. This acquisition system is a fixed focus system with a reported narrow depth of field of 5 cm. Compared to traditional desktop/wall mount systems (such as those marketed by Panasonic, LG and others), this system has the advantage of an increased stand-off distance and reduced level of cooperation from the subject. However, iris acquisition fails if a subject's iris is not acquired through a fixed, small capture volume. This system uses a modular approach to increase the height of the capture volume, in which multiple cameras are stacked one above the other so that the iris can be captured irrespective of the height of the subject. The extra hardware and custom lenses increase the cost of the system.
Another category of acquisition systems involves the use of cameras which can be panned, tilted and zoomed. These cameras alleviate the constraint of a fixed capture volume. These systems are based on the use of multiple cameras—a first, wide angle scene camera to detect the face/eye in the scene and a second camera with a high magnification lens, specifically aimed to resolve the fine patterns in the iris. Depth estimation is performed using a stereo-camera setup. This information helps in estimating the position of the subject in 3D space and hence the focus and pan/tilt settings.
Yet another system uses a commercial off the shelf pan/tilt/zoom camera to track the faces of subject and to acquire irises when the subject is still. The subject's irises may be acquired from stand-off distances of up to 1.5 meters. This system uses a single camera setup to acquire both the face and iris from subjects of different heights. The Retica Eagle Eye system uses a scene camera, a face camera, and two iris cameras, which account for its large form factor. The capture volume of this system is larger compared to the systems described so far, yielding a 3 m×2 m×3 m capture volume, with increased stand-off (average of 5 m).